Exemplary embodiments of the present invention relates to an acoustic sensor apparatus and an acoustic camera for using MEMS microphone array.
An acoustic camera is an ultramodern measurement apparatus for visualizing sound, and a new technology device which is necessary in various fields such as multimedia information devices, household electrical appliances, automobiles, construction, etc. The applicant of the present invention, SM instruments Inc. and the KAIST are the one that have leading technologies in the acoustic camera for using the existing measurement microphone and have made common products.
Korean Registration patent number No. 10-051120 of ‘Korean Advanced Institute of Science and Technology’ is a method of separating sound filed of the separate sound source by using acoustic holograph, as a method of separating sound field of sound source for using acoustic holography, comprises a first step for measuring sound pressure at several points on hologram and for obtaining hologram spectrum matrix which comprises magnetic spectrum of sound pressure at each point and respective spectrum between respective points; a second step of applying the hologram surface spectrum matrix to the acoustic holography method and calculating a sound source surface spectrum matrix which comprises a magnetic spectrum of sound pressure value at each point and a mutual spectrum between respective points; a third step of determining as a position of sound source a position where the magnetic spectrum of sound pressure value is a maximum in the sound source surface spectrum matrix, and calculating contribution amount of the determined sound source, and a fourth step of renewing, if there is a remaining spectrum matrix which is a subtract of contribution amount of the determined sound source from the sound source surface spectrum matrix, the remaining spectrum matrix into a new sound source surface spectrum and repeating its performance from the third step.
Korean Patent No. 10-0217872 of ‘Korean Advanced Institutes of Science Technology’ discloses a visualization system of acoustic characteristic, as visualization system for acoustic characteristic which obtains hologram at any hologram surface 22 moving with a sound source for any acoustic characteristic having any wavelength of sound source radiating energy to the surroundings, and calculates acoustic characteristic estimated value in sound filed by using the hologram, comprising a sound source movement measuring means 11, 12; a receiving means 13 for receiving energy radiated from the sound source at the plural positions which are arranged in series at smaller interval than half of the wavelength of the acoustic characteristics in a vertical direction to the movement direction in the region, to generate signals representing the energy; a multiple transmission unit for outputting through one output line the multiple of input signals which comprises a movement direction and a movement velocity of the receiving means 13 and a movement direction and a movement velocity of the sound source which is inputted from the sound source movement measurement means 11, 12 and the signal generated from the receiving means 13; a calculating means 15 for acoustic characteristics estimated value in sound field from the estimated sound characteristics at the hologram 22 outputted from the multiple transmission means 14 wherein the calculating means 15 defines relative coordinates comprising a hologram coordinates which moves correspondingly to a movement direction and a movement velocity of sound source measured by the sound source movement measurement means 11, 12 and receiving coordinates which moves correspondingly to a movement direction and a movement velocity of the receiving means 13 in the region, and the calculating means calculates the acoustic characteristic estimated value in the sound field by fourier transforming for time according to equation no. 1, information for the receiving means 13 from the multiple transmission means 14 outputted as coordinate value in the receiving coordinates.
Korean Patent number 10-08318239 comprises an acoustic sensing unit for sensing sound generated at sound source; a background photographing unit for photographing background on which the sound source locates; a sound source signal generating unit for performing sequentially fourier transformation, beamformation and reverse Fourier transformation for acoustic signal detected at the acoustic sensor unit and for generating sound source signal which is acoustic signal and time signal at sound source surface where the sound source locates; a data generating unit for generating sound quality data at the sound source surface as loudness which is quantitive factor by performing ⅓ octave band analysis processing, a loudness weighted value application, and a processing for calculating overall loudness by determining loudness index at a certain loudness index; a sound quality display unit for displaying sound quality image data generated by overlaying the sound quality data and the image data of the background taken photograph at the background photographing unit.
Korean patent no. 10-2009-0047507 of SM instruments Inc., an apparatus and method for visualizing a moving noise source discloses an apparatus for visualizing a moving noise source comprising at least two pairs of photo sensor units, which locate facing each other on a same photo axis in order to measure acceleration of a noise source moving in a uniform acceleration, for detecting change of photo amount resulting from the passing of the noise source through the photo axis and for generating time signal for when the noise source passes the photo axis; a microphone array sensor unit for generating sound pressure signal by detecting noise from the noise source; a data collection unit connected to the microphone array sensor unit and the photo sensor unit, for collecting the time signal and the sound pressure signal; and a central processing unit connected to the data collection unit, for receiving the time signal and the sound pressure signal from the data collection unit and defining an imaginary sound surface on a side of a certain part of the noise source and outputting sound pressure signal at each grid of the imaginary sound source surface as beam power level corresponding to the sound pressure signal by using a beam formation method, and for outputting to a monitor by mapping the beam power level on an image of the noise source.
Generally, a capacitive microphone based on microelectromechanical system, hereinafter called MEMS microphone has an advantage of overcoming basic limitation of the existing electret condenser microphone, hereinafter called ECM.
A vibration plate having electrical or mechanical reaction in the MEMS microphone is made of dielectric substance such as polysilicon or silicon nitride film and silicon oxide film, and the plate has a reliability in a temperature from −40° C. to 120° C., and has a reliability even in complex temperature/humidity change. In addition, in a case of MEMS microphone using a silicon substrate, it endures even in lead-free surface-mount temperature over 260° C. Due to the above fact that it has a high reliability and it endures even in mount temperature, it surpasses the existing ECM. The ECM can be packed only in a can type, and however the MEMS microphone can be packed according to request of user, and it is suitable to applied fields of the microphone in which it has been minimized and integrated in the present. The MEMS microphone senses capacitive change according to sound pressure which is inputted when uniform DC bias voltage is applied between a vibration plate and a reference plate. The MEMS microphone can be made smaller than most miniature ECMs, and the MEMS microphone is less sensitive to mechanical vibration, temperature change, or electromagnetic field interference than the ECMs. Due to the advantageous characteristics, the microphone is more used not only for hearing instruments or electronic stethoscope but also for cellphone, notebook computer, camcoder and a digital camera, etc.
As described, the microphone array beamformer is a method of searching position of noise source, and it is a method of measuring sound wave generated at noise source by the plural of microphone sensors and showing distribution of noise source like a photograph by processing the signals. It comprises measuring magnitude of sound pressure by restructuring according to characteristics of signals transmitted from each microphone into signals generated at a certain transmission position, and showing the measured sound pressure level as distribution in space to presume position of noise source.
The measurement method of the acoustic camera has been developed for research in special fields, and however due to the advantage of checking distribution of noise source it is also used for research/development in many industry fields.
FIG. 4 shows measurement examples of a microphone array in an abroad research. An area described in red in a noise source distribution shown with a photograph of test object, is the one where strong noise is generated. Through the graph, users can determine by intuition where noise is generated. The existing products in the conventional art use more than 30 expensive measurement microphones and expensive data measurement apparatus, and thereby making products complex and very expensive. One product costs about 100 million dollars FIG. 5 shows a conventional system.